Ultrasonic thermometers for measuring high temperatures and temperature profiles are known in the art and have become more important with increased research at high temperatures. These ultrasonic thermometers operate by sensing changes in the velocity of reflected sound waves propagated through a sensor in contact with the object for which the temperature is desired to be known.
Generally, ultrasonic thermometers consist of an electromagnetic coil surrounded magnetostrictive iron-cobalt head welded to a thoriated tungsten wire which comprises the means by which the heat is sensed. At the tip of the thoriated tungsten wire heat sensor are small notches or discontinuities formed at regular intervals. The portion of the thoriated tungsten wire sensor in contact with the matter which temperature is to be measured is usually contained in a protective tungsten sheath.
The electromagnetic coil surrounding a portion of the magnetostrictive iron-cobalt head is pulsed with an electrical pulse generating a pulsed magnetic field which produces acoustic or sound pulses in the magnetostrictive head. These sound pulses are propagated through the magnetostrictive head to the thoriated tungsten wire sensor which continues the acoustic pulse along the wire sensor to the area of the notches. Each time it passes a pair of formed notches or discontinuities in the wire sensor, a reflection of part of that acoustic pulse is sent back to the magnetostrictive head. Such procedures continue with each notch until the sound pulse reaches the end or tip of the sensor at which time it is returned back to the magnetostrictive iron-cobalt head.
As the pulses from each pair of notches return to the magnetostrictive head, it is sensed by the electromagnetic coil, such signals then amplified and sent on to a signal-processing console for conversion to temperature data. Since the velocity of the reflected pulses between adjacent notches is dependent upon the temperature of the thoriated tungsten wire sensor between the notches, the time between reflected pulses can be translated into an average temperature between adjacent notches.
Problems however have existed in these ultrasonic thermometers due to factors such as maintaining accuracy of the temperature measurements over extended periods of time between different tests and where the equipment may be subject to handling by technicians. It is usual that long and involved calibrating procedures are necessary between tests because of the dependence of the readings upon mechanical factors in the construction and maintenance of the thermometer leading to errors induced by repeated handling by technicians.
Misalignment of the elements of the ultrasonic thermometers in small amounts can easily result in sensed temperature variation errors of .+-.50.degree. C. Similarily, errors in observed temperatures can occur when the fixture itself holding the elongated wire sensor relative to the pulsing element interferes with the propagation of the ultrasonic signals.
In addition, it has been observed that improper coupling of the elements of prior art ultrasonic thermometers make vast changes in the sensed temperatures for repeated tests leading to inaccuracies in test results.
Another problem area the solution of which has eluded investigators in the past is how to deal with tip reflection, i.e., signal reflection at the end of the elongated wire sensor, since the variation of magnitude of the tip reflection due to coupling and other factors is relatively large in comparison with the other reflected signals. In fact, the general conclusion is that information from end reflection is useless because of the difficulties encountered in trying to reproduce coupling conditions from test to test.
It is to the solution of these problems which the improved invention is directed in order to facilitate accurate and repeatable results not affected by technicians handling or variances in element fabrication and coupling.